In the field of industrial automation such as electric drive and motor drive, mechanical resonance is common and the resonance frequency is generally about several hundred Hertz. Mechanical resonance may bring many disadvantages, for example, high on-site noise level, degradation of machining precision and mechanical precision, or shortened service life of the machines, etc. Therefore, it is required to remove the mechanical resonance as possible as we can when a machine is working, in particular, when high precision controls, such as a servo driver, are employed.
Generally, a servo driver comprises a resonance restraining controller therein and the resonance restraining controller would reduce the strength of the resonance frequency significantly if the resonance frequency is predetermined correctly. As such, the disadvantages of the mechanical resonance may be eased effectively. Therefore, it is essential to predetermine the correct mechanical resonance frequency. Generally, the mechanical resonance frequency is in a range of 100 Hertz to 1,000 Hertz, and if the precision of identification is less than 5 Hertz, it would satisfy the requirements of various applications.
In the prior art, a conventional method of identifying mechanical resonance frequency is implemented using an upper device. When a mechanical vibration is generated, the actual speed signal of the motor is collected by the upper device where the time domain signals are subjected to frequency analysis by Fast Fourier Transform (FFT) to obtain the amplitudes of each of the frequency points, and the frequency which corresponds to the greatest value of the amplitudes is the mechanical resonance frequency. However, this solution has the following problems: the frequency resolution of FFT is relative to the data size of the collected signal. If a higher resolution of frequency is required, the data size that needs to be collected would be greater. However, the amount of calculation of FFT will be increased by geometrical progression with respect to the collected data size. With the limitation of large amount of calculation, the upper device is generally a PC. In addition, other auxiliary devices are required, such as communication cables between the upper device and the servo driver, special servo communication software installed in the upper device, which complicate the overall device structure and increase the overall costs. Another problem is that the method of identifying mechanical resonance frequency as described above requires that the on-site operators are trained and have relevant skills, which, generally, can not be satisfied. Accordingly, it is rarely found that the on-site operators measure the mechanical resonance frequency using the upper device.
From the views of intelligent level and ease of use of a servo driver, if the function of resonance frequency identification is available to the servo driver per se, the mechanical components can be better driven, and the control performance of the servo driver can also be improved.